Abstract:
Reciprocal acoustic transmissions made in a region just south of the Gulf Stream
are analyzed to determine the structure and variability of temperature, current
velocity, and vorticity fields at the northern extent of the southern recirculation
gyre. For ten months (November, 1988 through August, 1989), a pentagonal array
of tomographic transceivers was situated in a region centered at 38°N, 55°W as
part of the eastern array of the SYNOP (SYNoptic Ocean Prediction) Experiment.
The region of focus is one rich in mesoscale energy, with the influence of local Gulf
Stream meandering and cold-core ring activity strikingly evident. Daily-averaged
acoustic transmissions yielded travel times which were inverted to obtain estimates
of range-averaged temperature and current velocity fields, and area-averaged relative
vorticity fields. The acoustically determined estimates are consistent with
nearby current meter measurements and satellite infrared imagery. The signature
of cold-core rings is clearly evident in the sections. Spectral estimates of the fields
are dominated by motions with periodicities ranging from 32-128 days. Second-order
statistics, such as eddy kinetic energies, and heat and momentum fluxes, are
also estimated. The integrating nature of the tomographic measurement has been
exploited to shed some light on the radiation of eddy energy from the Gulf Stream.
The Eliassen-Palm flux diagnostic has been applied to an investigation of wave
radiation from the Gulf Stream. Results of the diagnosis suggest that the Gulf
Stream itself is the source of wave energy radiating into the far field and found in
the interior of the North Atlantic subtropical gyre.
